Various optical systems have been developed for estimating the distance to and shape of objects. These are sometimes referred to as rangefinders, range sensors, and depth map cameras. Here, they will be referred to as “rangefinders.” A rangefinder estimates distances to one or more regions within a scene. The scene can contain one or more objects.
Some rangefinders estimate depth by analyzing the blur that is present in at least one image of the scene. Examples of such rangefinders are described in S. K. Nayar, M. Watanabe, and M. Noguchi, “Real-Time Focus Range Sensor,” IEEE Transactions on Pattern Analysis and Machine Intelligence, vol. 18, no. 12, 1186-1198 (December 1996), S. Bae and F. Durand, “Defocus Magnification,” Computer Graphics Forum, 26, 571-579 (2007), G. C. Birch, J. S. Tyo, and J. Schwiegerling, “3D Astigmatic Depth Sensing Camera,” Proc. SPIE 8129, Novel Optical Systems Design and Optimization XIV, 812903 (Sep. 9, 2011), and in J. H. Elder and S. W. Zucker, “Local Scale Control for Edge Detection and Blur Estimation,” IEEE Transactions on Pattern Analysis and Machine Intelligence, vol. 20, no. 7, 699-716 (July 1998)
Existing rangefinders have various disadvantages. For example, time-of-flight, structured illumination, or existing depth-from-defocus devices, are typically undesirably sensitive to ambient light and object color or reflectivity, provide infrequent depth data, are too expensive for certain applications, or have insufficient depth accuracy.
Thus, to obtain range information of the scene in a manner that cures at least some of these disadvantages, another approach to obtaining depth information must be used.